The transmission of high frequency electrically transmitted signals often requires a shielded cable to prevent signal interference or noise resulting from ambient EMI/RFI. The shielding typically may be provided by an electrically conductive braid that surrounds an array of individual insulated conductors within the cable. The braid will extend the entire length of the cable except for the ends where the cable will be appropriately dressed to enable the conductors therein to be electrically connected to the terminals of a connector.
The above described shielded cables and associated connectors frequently are used in military applications and other applications requiring high frequency electrical signal transmission. In many such applications the connector/cable interface should be environmentally sealed and should provide a superior strain relief connection to ensure that the quality of the electrical connection is not affected by any physical abuse to which the connector and cable might be subjected. Furthermore, the electrical and mechanical termination of the cable in the connector should ensure that the EMI/RFI shield continues through the connector despite the required termination or dressing of the cable end. The cable/connector interface should also account for the inevitable fact that the termination and connection work often will be performed by field personnel working in substantially uncontrolled environments with possible limited access to tools.
The connectors for the above described shielded cable, as used in the above described environments, typically have been provided with backshell and frontshell combinations that are mechanically connectable to one another. The backshell is further mechanically mounted to the cable, while the frontshell is mechanically mounted to a connector housing. Both the backshell and frontshell have been formed from metallic material, and the backshell has further included appropriate electrically conductive means for engaging the cable braid to ensure that the EMI/RFI shield continues through the backshell, the front-shell and the remainder of the connector assembly. Although many prior art backshell assemblies have provided adequate EMI/RFI shielding for the above described braided cables, they have either not provided adequate strain relief and environmental sealing, or have relied upon complex multi-component structures for achieving strain relief and environmental sealing.
One grounding backshell is shown in U.S. Patent No. 3,739,076 which issued to Schwartz on June 12, 1973. The connector shown in U.S. Patent No. 3,739,076 comprises a rearwardly projecting neck portion having an array of externally disposed threads thereon. An end member or backshell is provided with an array of internal threads for threaded engagement over the rearwardly projecting neck of the connector. A coil spring formed into a generally toroidal configuration is disposed intermediate the rearwardly projecting neck of the connector and the backshell. The toroidal spring is further disposed to be aligned with the exposed conductive braid of the dressed cable. The threaded engagement of the rearwardly projecting neck of the connector with the backshell radially compresses the toroidal spring into electrical contact with the braid. The toroidal spring thus electrically grounds the braid to the backshell and connector housing to achieve a continuous EMI/RFI shielding across the connector. The connector shown in U.S. Patent No. 3,739,076 is further provided with an O-ring disposed intermediate the toroidal spring and the backshell. The O-ring is intended to achieve environmental sealing of the connector. However, the O-ring is disposed at a location within the connector that would permit the accumulation of moisture or the like inside a portion of the connector assembly. It generally is desirable to keep moisture and other such environmental contaminants entirely out of the connector structure if possible. In many instances, a single O-ring disposed within a connector is not considered sufficient environmental sealing. Furthermore, the O-ring is not intended to and cannot achieve strain relief, and the connector shown in U.S. Patent No. 3,739,076 does not provide any alternate means for achieving the necessary strain relief.
Other prior art connectors have included variations of the structures shown in U.S. Patent No. 3,739,076. For example, one such prior art connector includes a metallic ground ring secured intermediate the backshell and a threaded adapter. The ground ring is dimensioned to electrically ground the braid of the cable. These other prior art backshell connector assemblies have relied upon internally disposed O-rings, grommets, washers or the like to achieve some degree of environmental sealing. Strain relief has been provided by separate cable clamps which are connectable to the prior art backshell. For example, an adapter which is engageable with the prior art backshell may include a rearwardly directed array of external threads. A strain relief clamp may include a corresponding array of internally disposed threads which are engageable with the threads of the adapter. The strain relief clamp further comprises a rearwardly disposed cable clamp which comprises a pair of bolts extending generally transverse to the cable and on opposite sides thereof. The strain relief clamp is first threaded onto the adapter and then the transversely extending bolts are tightened to urge clamping members into a tight strain relief clamping engagement with the cable. Prior art backshell connector assemblies of this general type are undesirable because of the complex plural components required. Furthermore, the assembly is time-consuming and complex and requires field personnel to utilize several different tools.
In view of the above, it is an object of the subject invention to provide a grounding backshell with improved strain relief.
Another object of the subject invention is to provide a grounding backshell which achieves exceptional environmental sealing.
Still another object of the subject invention is to provide a grounding backshell that can be easily assembled by field personnel.
An additional object of the subject invention is to provide a grounding backshell with means for simultaneously providing environmental sealing and strain relief.
A further object of the subject invention is to provide an environmentally sealed strain relief backshell which simultaneously provides grounding to a shielded cable in one single connecting operation.